Project Summary This prospective clinical cohort study will examine the association of HIV pre-exposure prophylaxis (PrEP) initiation and subsequent patterns of condom-use and sexually transmitted infections (STIs) in men who have sex with men (MSM). The cohort, comprising ~ 600 MSM, 18 years and older, who initiate PrEP and receive services from a sexual health clinic in San Francisco, will be followed quarterly for 12 months. PrEP, in the form of Truvada, is a once daily pill, which is simple to use with low toxicity and good efficacy in reducing the risk of HIV acquisition. While PrEP addresses protection against HIV transmission, it does not provide any protection against other STIs, MSM are disproportionally affected by STIs, and rates continue to increase in this population8-10. This study will examine condom-use change and STIs in a high risk population of MSM taking PrEP. It will provide information on potential disease prevention strategies and health promotion messages that encompass social and individual influences on safe sex practices. In this study, the theories of Sexual Scripting and Reasoned Action will be used as a framework to guide the understanding of the social and individual influences on voluntary risk behavior and sexual practices among MSM. The aims of this study are: 1) To examine the associations between levels of risky behaviors in a cohort of MSM prior to initiating PrEP versus those behaviors over 12 months subsequent to initiating PrEP; 2) To identify changes in condom use and examine reasons for change; and 3) To determine changes in risk behaviors in MSM who are initiating PrEP using biological assays to measure the frequency and type of STIs. After frequencies and descriptive analyses are completed, multilevel logistic regression models will be used to predict the associations of risk behaviors before and after initiation of PrEP with demographic variables. Latent variable growth modeling (LGM) will be utilized to describe growth curves for condom use and STIs in order to understand not only the average change but also individual variations. Qualitative interviews will be conducted with a sample of 10-20 individuals to enrich our knowledge and understanding of the social influences and individual motivations that may be affecting condom-use. This study will capture sociodemographic data among PrEP users, their reasons for using PrEP, and the societal, psychological and behavioral influences on condom use and subsequent changes in STIs during a real-world implementation of a PrEP health program. Information gathered in this research will fill a knowledge gap on MSM using PrEP, condom-use and STIs. It will lay the foundational work for the development of a sexual health intervention for MSM on PrEP in order to improve condom use behavior and decrease STI rates. This study will be completed with the support and expertise from my interdisciplinary mentorship team. Drs. Portillo, Carrico, Boyer, Milo-Santos have a wide range of advanced knowledge in sexual health, MSM, risk behavior, statistical methods, qualitative and quantitative research and are committed to my successful training as a nurse researcher.